When two electronic devices are connected, it is often of advantage to use the same electric signal line for different purposes. USB signal lines, for example, may be used to transfer audio signals.
Specifically, portable media players (PMPs) generally have USB interfaces, for connecting the PMPs to interoperable devices, such as USB cameras, USB card readers and USB hard drives. Due to size limitations, the same USB connector may be used for both USB data and audio output, and a multiplexor (MUX) is used to separate the USB signals from analog audio output.
In this regard, reference is made to FIG. 1, which is a prior art illustration of a general analog/digital switching device 100 that can also be used for routing USB 1.1 signals. Switching device 100 is a low voltage, CMOS device manufactured by Analog Devices of Norwood, Mass. As shown in FIG. 1, switching device 100 includes two independently selectable single-pole double-throw (SPDT) switches.
Switching devices such as the device shown in FIG. 1 are not flexible enough to support configurations where both of the connected USB devices have their own audio interfaces. In such case, multiple audio configurations may exist, and a more intelligent switching device is required to route the analog audio signals and the digital USB signals.